1. Field of the Invention
The present invention relates to sputtering methods for forming films, and more particularly, relates to a sputtering method for forming a transparent conductive film using a reactive sputtering process such as a DC sputtering process provided with a transfer mechanism.
2. Description of the Related Art
In general, as a sputtering method for forming a transparent conductive film on a substrate, there have been proposed a sputtering method using a target composed of an In2O3-SnO2-based material in an argon (Ar) atmosphere and a reactive sputtering method using a target composed of an Inxe2x80x94Sn alloy in a mixture of Ar and oxygen (O2).
In the former method described above, a film having low electrical resistance and a high transmittance can be obtained immediately after the completion of sputtering; however, it has been difficult to increase the film-forming rate.
In contrast, in the case of the latter method, i.e., in the reactive sputtering method, the film-forming rate can be increased. In particular, in a DC magnetron sputtering apparatus using a cylindrical rotating target disclosed in for example, U.S. Pat. Nos. 4,356,073 and 4,422,916, it has been believed that the usage efficiency of the target material is approximately 2.5 to 3 times that of a conventional planar type target (KINOU ZAIRYO (Functional Material), Vol. 11, No. 3, pp. 35-41, March, 1991).
The high usage efficiency described above means that the cylindrical rotating target described above used for the reactive sputtering method can reduce the cost of target material used and, in addition, can also reduce the apparatus downtime due to target replacement. Accordingly, it is believed that the DC magnetron sputtering apparatus using the rotating target described above can be suitably used as a mass-production apparatus. However, in this reactive sputtering method, since the optimum film-forming conditions, in particular, the optimum gas flow volume, are limited to quite narrow ranges, it has been extremely difficult to properly control the film formation.
As a method which can overcome the disadvantage described above, a reactive sputtering method using a plasma emission monitor (hereinafter referred to as PEM) has been well known, which is disclosed in xe2x80x9cProgress in the Application of the Plasma Emission Monitor in Web Coatingxe2x80x9d by S. Schiller, U. Heisig, Chr. Korndorfer, J, Stumpfel, and V. Kirchhoff (Proceedings of the 2nd. International Conference on Vacuum Web Coating, Fort Lauderdale, Fla., USA, October 1988).
The PEM is a monitoring device for monitoring a plasma state by an electrical signal obtained from plasma emission which is condensed by a collimator and is then photoelectrically transferred by a photomultiplier via a spectroscope. One function of the PEM is to adjust the flow rate of a reactive gas so as to maintain the plasma emission intensity constant while the sensitivity of the photomultiplier is set at a predetermined value. For example, in order to form an ITO (indium tin oxide) film, the PEM controls the flow rate of a reactive gas (O2) So as to maintain the plasma emission intensity of In (wavelength of 451.1 nm) constant, whereby a film having a uniform quality can be obtained.
However, in the case described above in which the PEM is applied to a reactive sputtering process, when a transparent conductive film is continuously formed on a substrate for a long time using a target composed of an Inxe2x80x94Sn alloy, the film-forming rate monotonically increases with time.
The present invention was made to solve the problem described above, and an object of the present invention is to provide an improved film-forming method by sputtering which can stably form a film having uniform thickness and quality on a substrate even when sputtering is performed for a long time.
To this end, a sputtering method for forming a film on a substrate in accordance with one aspect of the present invention comprises a step of controlling a transfer speed of the substrate so as to compensate for the film-forming rate, and a step of controlling the amount of heat applied to the substrate so that thermal equilibrium of the substrate temperature is maintained.
In addition, an apparatus for forming a film on a substrate by sputtering in accordance with another aspect of the present invention comprises a transfer unit for transferring the substrate, a heating unit for heating the substrate, a thickness meter for measuring the thickness of the film formed on the substrate, and a controller for controlling the transfer speed of the substrate and the amount of heat applied to the substrate in accordance with the film thickness measured by the thickness meter, wherein the controller controls the transfer speed to compensate for the film-forming rate and controls the amount of heat applied to the substrate in accordance with the transfer speed so that thermal equilibrium is maintained at a temperature of the substrate.
According to the configuration described above, a film having a uniform thickness and quality can be stably formed on the substrate for a long time.